Dishwashing Machine With Heating Control

ABSTRACT

A dishwashing machine for commercial use to clean items cyclically has at least one tank for holding a dishwashing liquid, as well as at least one heating apparatus for heating the dishwashing liquid, and at least one temperature sensor for detecting the temperature of the dishwashing liquid. The dishwashing machine also has a controller being designed in order to control heating of the dishwashing liquid in at least one program step in a dishwashing program, with the heating being carried out at least until a predetermined intended temperature is reached. In this case, before or during an initial heating phase, a start temperature of the dishwashing liquid is detected, the minimum heating duration being determined from the start temperature. The heating process is then carried out accordingly with this minimum duration.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on German Patent Application No. 10 2007 005 834.0 filed 1 Feb. 2007, upon which priority is claimed, and on Provisional Application 60/907,302 filed on Mar. 28, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a dishwashing machine for commercial use, and to a method for controlling a dishwashing machine for commercial use.

2. Prior Art

Commercial dishwashing machines are used in various areas in which relatively large amounts of items to be cleaned have to be cleaned within a short time. These items to be cleaned may, in particular, be in the form of glasses, flatware, plates and dishes, containers, trays, saucepans and cooking pans, kitchen utensils or similar other objects. It is also feasible to clean other types of items to be cleaned, in particular including items from other areas than the area of large kitchens. However, in particular, machines such as these are used in the area of large industrial kitchens, for example in hospitals, works canteens, school canteens or restaurants.

In contrast to domestic machines, industrial dishwashing machines for commercial use are distinguished by achieving fast cycle times. In addition to so-called continuous-flow dishwashing machines, so-called automatic programmed machines are also used for this purpose, in which the item or items to be cleaned is or are cleaned in a dishwashing chamber, cyclically.

In order to achieve the required high throughput of dishes to be cleaned, automatic programmed dishwashing machines such as these for commercial use are designed for the particular feature of optimization of the time required for the individual program steps. For example, a predetermined nominal temperature must be used in order to achieve adequate cleaning. A similar situation also applies to final rinsing, which likewise necessitates a predetermined nominal temperature.

In order to achieve the short cycle times which are required for dishwashing machines for commercial use, dishwashing machines such as these frequently make use of two or more tanks, in contrast to domestic appliances, which are preferably arranged separately from one another and can be used for the individual program steps. This makes it possible, for example, to separately optimize the heating times of the individual dishwashing liquids which are used for dishwashing and/or final washing. In this case, the aim is preferably to minimize the heating time to that required to achieve the predetermined intended temperature. However, at the same time, it is necessary to ensure that this temperature is actually reached.

In order to solve this problem, EP 1 415 586 A2 describes a method and an apparatus in which the washing time can be deliberately lengthened. The items to be cleaned are cleaned in a circulation mode during a washing cycle, while a final washing liquid is heated for a predetermined minimum time, in parallel with this in time. Once the minimum time has passed, the final washing liquid is measured to determine whether it has already reached the necessary intended temperature, and if this is not the case, the washing cycle is appropriately lengthened.

In many cases, the result of a method such as this is unsatisfactory, however. As before, the minimum time is an unknown variable based essentially on empirical values. If this preset time is inappropriate, then, for example, heating power may be wasted thus in turn lengthening the washing cycle or, on the other hand and in the worst case, regular temperature monitoring can be started shortly after the start of the circulation step which, in the final analysis, represents nothing more than temperature monitoring from the start of this circulation step.

OBJECT AND SUMMARY OF THE INVENTION

The object of the present invention is therefore to propose a dishwashing machine as well as a method for controlling this dishwashing machine, which avoid the disadvantages described above of the prior art, and which is designed in order to achieve cycle times which are as short as possible and at the same time to minimize the use of heating energy.

The invention will be described in the following text with reference to the proposed dishwashing machine, which has a controller. All of the method features implemented in the controller may, however, be used independently of this dishwashing machine and of the controller.

The proposed dishwashing machine is designed in order to clean items to be cleaned in a dishwashing chamber, cyclically. The items to be cleaned may, for example, be the types of item to be cleaned as described above.

The dishwashing machine has at least one tank for holding a dishwashing liquid, as well as at least one heating apparatus for heating this dishwashing liquid, and at least one temperature sensor for detecting the temperature of the dishwashing liquid.

Furthermore, as described above, the dishwashing machine has a controller which is designed in order to carry out and to control a dishwashing program. For example, this controller may have one or more electronic components, for example an appropriately programmed computer (for example a microcomputer). Further elements may also be provided, such as input and output means (for example a display, a keyboard, an interface), as well as one or more volatile and/or non-volatile data memories.

In at least one program step, the controller controls the heating of the dishwashing liquid. This heating process is continued at least until a predetermined intended temperature is reached.

In contrast to the prior art, it is proposed that a start temperature of the dishwashing liquid be detected at the start (that is to say before the start of the heating process and/or in an initial phase of the heating process). For example, the dishwashing machine may provide one or more temperature sensors for this purpose.

A minimum heating duration is then determined from this start temperature. The heating is then carried out accordingly using this minimum duration. In contrast to the prior art, no arbitrary minimum duration based on an empirical value is predetermined, and, instead, the minimum duration is determined on the basis of the start temperature. This may, be done analytically or semi-empirically, in particular with the initial variables for this determination process being the amount of liquid M of the dishwashing liquid to be heated (quoted, for example, in kg), a specific thermal capacity c of the dishwashing liquid to be heated (quoted, for example, in J/(kg K)), the temperature difference between the intended temperature Tz and the start temperature T_(S) (quoted, for example, in K) and the heating power P (quoted, for example, in W) of the heating apparatus. By way of example, the minimum duration t_(min) (quoted, for example, in s) may be calculated using the following formula:

$t_{\min} = \frac{c \cdot \left( {T_{2} - T_{1}} \right) \cdot M}{P}$

The formula described above for determining the minimum duration can be further optimized by taking account of heat losses. These heat losses may be determined empirically, semi-empirically or analytically by thermal radiated emissions, steam output or else by other loss mechanisms, for example by taking account of known material characteristics or by comparing heating times calculated using the idealized formula quoted above with measured heating durations. For example, analytically, the minimum heating time would be calculated as the solution of a differential equation in which the total amount of heat introduced per unit time will be considered to be the difference between the heat introduced by the heating apparatus minus the heat removed per unit time as a result of heat losses (depending, for example, on the difference between the current temperature of the dishwashing liquid and the ambient temperature, as well as a thermal conductivity coefficient).

Alternatively or additionally, the use of correction variables is proposed as a simple method for taking account of heat losses. For example, his may be a correction factor relating to the formula quoted above, a correction function, a correction characteristic or a similar correction algorithm. For example, appropriate correction characteristics can be stored in an electronic data memory. These correction factors may also be appropriately temperature-dependent, in order to take account, for example, of the temperature dependency of heat losses.

The controller can also be designed to detect the temperature of the dishwashing liquid once again after the minimum duration has elapsed. The heating process can then be extended in a subsequent decision step, if the temperature is below the intended temperature, or is below this intended temperature by more than a tolerance threshold. If the temperature has reached or exceeded the intended temperature, then the heating can be ended.

This checking of the temperature of the dishwashing liquid may, in particular, also be repeated if the intended temperature has not yet been reached. The described decision step can then also be repeated, and this process can be continued until the intended temperature is reached, or the temperature is within a tolerance threshold below the intended temperature.

The described dishwashing machine and the described program in one of the described refinements has the advantage over the dishwashing machines and methods know from the prior art that a predetermined intended temperature can be reached reliably and quickly. This makes it possible, for example, to safely comply with hygiene parameters in accordance with the relevant Standards and Regulations. Examples of Standards such as these are: DIN 10511: Foodstuffs hygiene, commercial dishwashers with glass washing machines; DIN 10512 Commercial dishwashers with single-tank dishwashing machines; DIN 10522: Foodstuff hygiene, commercial machine washing of multiple-use boxes and multiple-use containers for unpackaged foodstuffs; EN ISO 15883-1: Cleaning and disinfection appliances; NSF/ANSI Standard 3: Commercial Warewashing Equipment (USA), hygiene test with thermo-label. Furthermore, overall, the proposed dishwashing machine makes it possible to greatly improve, and therefore optimize, the washing and final washing result. During the process, the items to be cleaned are dealt with carefully.

As described above, the dishwashing machine can advantageously in particular have at least one washing tank and one circulation device for initial cleaning of the items to be cleaned, as well as at least one final washing tank for final washing of the items to be cleaned. As mentioned initially, this has the advantage that (in contrast to domestic appliances), heating processes can be carried out in parallel.

The principle as described above for determining the minimum duration can in this case be used both for heating of the washing tank and—alternatively or additionally—for heating of the final washing tank.

Use in the final washing tank has the advantage, for example, that the best final washing result is achieved at a high temperature. Furthermore, subsequent drying of the items to be cleaned is greatly improved. In addition, the final washing water is in many case introduced into the washing tank after use, this avoids the washing tank being cooled down by excessively cold final washing water. A further advantage is that the final washing liquid in many cases has additives mixed with it which, for example, allow the items to be cleaned to be wetted better. However, the effect on these additives is temperature-dependent. If the temperature of the final washing liquid is chosen to be too low, then this results in poorer wetting of the items to be cleaned, and possibly in the formation of foam.

The application of the described principle to the heating of the washing tank has the advantage that it is possible to optimize the washing effect and the washing result, which is generally ensured only at the correct temperature. In particular, the washing liquid at least has cleaners added to it. The effect of these cleaners is, however, once again dependent on the temperature, and, for example, the cleaners may saponify if the temperature is too low, with a corresponding deterioration of the cleaning result. Effects such as these can be effectively avoided by the described method and the proposed dishwashing machine.

By way of example, at least one program step in the described two-tank or multiple-tank dishwashing machine may comprise a circulation step, in which case the controller may be designed such that the dishwashing liquid being circulated is heated at least until the predetermined intended temperature is reached in the washing tank. During this circulation mode, it has been found to be particularly advantageous to detect the start temperature after a predetermined start delay rather than immediately at the start of the circulation step. The start temperature is preferably measured after a start delay of 5 to 60 seconds, in particular between 10 and 20 seconds. This advantageously makes it possible for the dishwashing liquid to be thoroughly mixed first of all in the washing tank in which, for example, there may initially be a temperature gradient from top to bottom, in order to result in an average temperature. In addition, the temperature of the items to be cleaned can be matched to the tank water temperature within the start delay, which means, overall, that the start delay makes it possible to measure an equilibrium temperature instead of a local non-equilibrium temperature. This greatly improves the method and the accuracy.

A further improvement to the dishwashing machine and to the proposed method may comprise the circulation step not being switched off immediately after the intended temperature is reached, but being continued for a predetermined action time. This improvement is particularly important when specific hygiene standards have to be satisfied (see for example the Standards quoted above). Standards such as these are defined, for example, by a predetermined minimum temperature acting on the items to be cleaned for a predetermined time period.

The above developments of the invention relate to the application of the idea of the invention in the circulation step and/or to the washing tank. As described above, the inventive idea may, however, alternatively or additionally also be applied to a final washing liquid. For example, the controller may be designed such that a final washing liquid in the final washing tank is heated while the initial cleaning process is carried out with washing liquid. In this case, in particular, the duration of the circulation step can be defined such that it corresponds to the specific minimum duration for heating the final washing liquid. This means that the initial cleaning is carried out, for example, until the final washing liquid has reached the predetermined intended temperature for the final washing liquid on the basis of the theoretical analysis described above. If it is then found after this minimum duration has been reached that the final washing liquid has not yet reached its intended temperature or is below the intended temperature by more than a tolerance threshold, then the duration of the circulation step can be lengthened. This process can also be carried out repeatedly until the intended temperature is reached, or a tolerance threshold is undershot.

If a final washing tank is used then the final washing liquid can be applied to the items to be washed in various ways in a final washing step. On the one hand, a pressure-increasing pump can be provided in order to increase the pressure of the final washing liquid and therefore to apply the final washing liquid to the items to be washed. Alternatively or additionally, however, pressurized fresh water can also be applied to the final washing tank via a fresh water connection, in order to use this pressure to apply the final washing liquid to the items to be cleaned. In the latter case, the final washing tank is still full, since the final washing liquid is displaced by the fresh water that is introduced. In the former case, for example, the final washing liquid tank may be completely or partially emptied, for example in the course of a two-level control process. It can then be replenished by time control or by level control.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and features of the invention will become evident from the following description of preferred exemplary embodiments, in conjunction with the drawings, in which:

FIG. 1 shows a schematic illustration of one exemplary embodiment of a dishwashing machine according to the invention;

FIG. 2 shows a refinement, as an alternative to the embodiment shown in FIG. 1, of a final washing tank with fresh water applied under pressure;

FIG. 3 shows one exemplary embodiment of a method according to the invention for controlling a dishwashing machine, in which a temperature in a washing tank is controlled, and

FIG. 4 shows a further exemplary embodiment of a method according to the invention, in which a temperature in a final washing tank is controlled.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The dishwashing machine 110 has a dishwashing chamber 112 in which items to be cleaned 114 can be placed. Furthermore, there is a nozzle system in the dishwashing chamber 112, comprising washing nozzles 116 and final washing nozzles 118. This nozzle system is in this case illustrated by way of example as a system of spraying arms arranged above and below the items to be cleaned 114. However, alternatively or additionally, it is also possible to provide different types of nozzles.

Furthermore, the dishwashing, machine 110 has a washing tank 120 which is designed to hold a washing liquid 122. The washing tank 120 may, for example, be equipped with one or more supply lines 124, for example in order to fill the washing tank 120 with fresh water and/or in order to supply a cleaning agent or dishwashing agent to the washing tank 120. In the illustrated exemplary embodiment, the washing tank 120 is in the form of a separate washing tank, although embodiments are also feasible in which this washing tank 120 forms part of the dishwashing chamber 112 and, for example, is in the form of a depression in a bottom area of the dishwashing chamber 112.

A heating apparatus 126 is also provided in order to heat the washing liquid 122 in the washing tank 120. The temperature in the washing tank 120 can be detected by means of a temperature sensor 128.

The washing tank 120 is connected to the washing nozzles 116 via a system of circulation lines 130. These circulation lines 130 are indicated only schematically here, and additional pumps and/or valves can be provided, although these are not shown in FIG. 1.

A circulation pump 132 is provided in the system of circulation lines 130. This circulation pump 132 ensures that washing liquid 122 is supplied under pressure to the washing nozzles 116. An outlet 134 is provided in the dishwashing chamber 112, although it is indicated only symbolically here. Washing liquid 122 can be returned via this outlet 134 from the dishwashing chamber 112 to the washing tank 120. The items to be cleaned 114 can then be washed in a circulation mode via this system of circulation lines 130 and the circulation pump 132.

Furthermore, as shown in the schematic exemplary embodiment in FIG. 1, the dishwashing machine 110 has a final washing tank 136. This final washing tank 136 holds a final washing liquid 138. For example, this may be fresh water, which is supplied to the final washing tank 136 via a fresh water supply 140. The final washing liquid 138 can be passed via a system of final washing lines 142 to the final washing nozzles 118 in order to provide final washing for the items to be cleaned 114—preferably after completion of the circulation mode described above. By way of example, further additives can be mixed with the final washing liquid 138 for this purpose, for example a rinse aid.

There are a number of possible ways to supply the final washing liquid 138 under pressure to the final washing nozzles 118. In the exemplary embodiment illustrated in FIG. 1, fresh water is introduced into the final washing tank 136 via the fresh water supply 140 and a fresh water valve 144 via a free-running section 146. The final washing tank 136 may, for example, be equipped with level sensors (not illustrated in FIG. 1), for example in order to provide two-level control.

During the final washing phase, the final washing tank 136 is at least partially emptied. The pressure increase which is required to allow the final washing liquid 138 to be supplied to the final washing nozzles 118 is in this case produced by a pressure-increasing pump 150. The pressure-increasing pump 150 can be driven, in the same way as the fresh water valve 144 as well, by a controller 152.

As an alternative to the embodiment illustrated in FIG. 1 with a final washing tank 136 which is partially emptied during the final washing process and is filled without the use of pressure via a free-running section 146, it is also possible to use the final washing tank 136 as illustrated in FIG. 2 for the dishwashing machine 110 as illustrated in FIG. 1. In this case, the final washing tank 136 is replenished with pressurized fresh water via the fresh water supply 140 and the fresh water valve 144, thus partially displacing the final washing liquid 138 in this final washing tank 136. In this case, there is no need for a pressure-increasing pump 150 and, instead, the line pressure in the fresh water supply 140 is sufficient to pass the final washing liquid 138 to the final washing nozzles 118, and to achieve the appropriate spraying effect there. The final washing tank 136 is continuously refilled in this process. Furthermore, the controller 152 can be used to operate the fresh water valve 144 (and therefore the final washing process).

Like the washing tank 120, the final washing tank 136 is also equipped with a heating apparatus 148. Furthermore, at least one temperature sensor 154 is provided in the final washing tank 136, and passes temperature signals to the controller 152. The controller 152 can also be designed to operate the heating apparatus 148.

A normal program which takes place in the dishwashing machine 110 may, for example, be designed such that washing liquid 122 is first of all circulated from the washing tank 120 in a circulation mode, in order to initially clean the items to be cleaned 114. In this case, instead of being in the form of a separate washing tank 120 (as illustrated in FIG. 1), the washing tank 120 may also be part of the dishwashing chamber 112. The controller 152 can be designed to operate all the valves, the heating apparatus 126 for the washing tank 120, and the circulation pump 132.

After completion of the circulation mode, the washing liquid 122 can be disposed of via an outflow 156. By way of example, two valves 158, 160 can be provided for this purpose, by means of which it is possible to switch from circulation through the circulation lines 130 to an outlet through the outflow 156. Furthermore, the temperature of the washing liquid 122 can also be monitored by means of a temperature sensor 162 arranged within the dishwashing chamber 112.

After completion of the circulation mode, the process then switches to the final washing mode. By way of example, the controller 152 is for this purpose used to start the pressure-increasing pump 150 or—as shown in the exemplary embodiment in FIG. 2—the final washing process can be started by opening the fresh water valve 144.

As described above, the controller 152 may, for example, be in the form of a microcomputer in which an appropriate program can run. The controller can preferably be used to check all of the information provided by the dishwashing machine 110 (for example signals from the temperature sensor 128, 154 and 162), and all of the valves (for example the valves 144, 158, 160) can preferably be controlled by the controller 152.

FIGS. 3 and 4 show schematic flowcharts of preferred exemplary embodiments of program procedures according to the invention, which can be carried out by means of the controller 152. In this case, FIG. 3 shows a program configuration in which the heating of the washing liquid 122 is monitored and/or controlled, while in contrast FIG. 4 shows an exemplary embodiment in which the temperature of the final washing liquid 138 in the final washing tank 136 is monitored and/or controlled. The two exemplary embodiments can also be combined in order to monitor and/or to control the heating of both the washing liquid 122 and of the final washing liquid 138.

In a first method step in the exemplary embodiment shown in FIG. 3, the circulation mode is started first of all (step 310). As described above, this can be done, for example, by appropriately driving the circulation pump 132. Further method steps associated with the circulation mode, for example filling of the washing tank 120 via the supply lines 124 or supplying an appropriate dishwashing agent, are not illustrated in the simplified method flowchart shown in FIG. 3.

A check is carried out in method step 312 to determine whether a predetermined start delay has been reached. As described above, the start delay is used, for example, to produce a temperature equilibrium in the dishwashing chamber 112, so that a temperature is achieved only after thorough mixing of the washing liquid 122 and temperature matching of the items to be cleaned 114.

If the start delay has not yet been reached (branch 314), then another check is carried out after a delay of a time interval 316 to determine whether the start delay has been reached. If the start delay has now been reached branch 318 in FIG. 3), then a start temperature of the washing liquid 122 is measured in step 320. This measurement may be carried out, for example, by means of the temperature sensor 128 in the washing tank 120, and/or via the temperature sensor 162 in the dishwashing chamber 112.

The minimum duration of the heating process for the washing liquid 122 by means of the heating apparatus 126 is then determined on the basis of this start temperature 320 in method step 322. For this purpose, various initial variables and correction variables are read, as indicated symbolically by the reference number 324 in FIG. 3. As described above, this determination of the minimum duration for heating can be calculated for example using the heating power of the heating apparatus 126, the thermal capacity of the washing liquid 122, the amount of washing liquid 122 and the temperature difference between the intended temperature to be achieved and the start temperature, preferably taking account of heat losses by means of appropriate correction variables (for example correction factors). For example, the initial and correction variables can be read 324 from a data memory for the controller 152, and/or individual variables can also be read directly, such as the start temperature, having been determined by means of the temperature sensor 128 and/or the temperature sensor 162.

The washing liquid 122 is then heated by the heating apparatus 126 in method step 326. However, instead of the sequential process illustrated in FIG. 3, this heating process 326 can be started in advance, for example immediately after the start 310 of the circulation mode. This ensures that the heating process 326 is started as early as possible, and this can speed up the heating process.

A check is once again carried out in method step 328 to determine whether the minimum duration determined in step 322 has been reached. If this is not the case (branch 330 in FIG. 3), then another check 328 is carried out after a delay interval 332 has passed, within which the heating process continues. If the minimum duration has been reached (branch 334 in FIG. 3), then the temperature of the washing liquid 122 is once again measured, in method step 336, by means of the temperature sensor 128 and/or the temperature sensor 162.

A check is carried out in method step 338 to determine whether the temperature measured in step 336 has reached the intended temperature. Alternatively, the intended temperature can also be predetermined with a tolerance threshold which should not be undershot. If the intended temperature has not been reached (branch 340 in FIG. 3), then another temperature measurement is carried out in step 336 after a predetermined delay 342 (which could also be dynamically adapted, for example in order to reduce this delay if the discrepancies are only minor), during which the washing liquid 122 is heated further. The check in step 338 is then carried out again.

If this intended temperature has been reached (branch 344 in FIG. 3), then this intended temperature can optionally be maintained for an action time 346, for example in order to satisfy a specific hygiene standard. The circulation mode can then be ended, in step 348. This is then followed by an appropriate final washing program step.

FIG. 4 shows one exemplary embodiment with monitoring/control of the heating process for the final washing liquid 138 in the final washing tank 136. After the start of the program in step 410, the circulation mode 412 is started for the washing liquid 122 (see above). A start temperature of the final washing liquid 138 is determined in parallel with this, in step 414, by means of the temperature sensor 154. Analogously to method step 322 in FIG. 3, this is used to determine the minimum heating duration for the final washing liquid (step 416). Once again, analogously to method step 324 in FIG. 3, initial and correction variables can be read for this purpose in step 418.

The heating of the final washing liquid 138 is then started in step 420. However, analogously to method step 326 in FIG. 3, this heating process can actually be started with the start 410, in order to avoid any time delay.

Analogously to method step 328 in FIG. 3, a check is then carried out in method step 422 to determine whether the minimum duration determined in step 416 has been reached. If this is not the case (branch 424), then another check is carried out after a delay 426. It should be noted that the method steps 422, 424 and 426, in the same way as the method steps 328, 330 and 332 in FIG. 3 as well, can also be replaced by a comparatively simple “wait function.”.

If the minimum duration has been reached (branch 428), then the temperature of the final washing liquid 138 is measured, in method step 430, by means of the temperature sensor 154. Analogously to method step 338 in FIG. 3, a check is then carried out in method step 432 to determine whether the final washing liquid 138 has reached the intended temperature. If this is not the case (branch 434 in FIG. 4), then the temperature of the final washing liquid 138 can be measured 430 again after a delay 436 (which, for example, can also once again be dynamically adapted in order to take account of the actual difference between the current temperature and the intended temperature). Once the intended temperature has been reached (branch 438), then the circulation mode can be ended in method step 440. The final washing step is then started immediately after this, for example in method step 442.

As described above, the method steps illustrated in FIGS. 3 and 4 may be implemented in the controller 152 for example in the form of programs. The method variants can also be carried out combined. A procedure as represented by the step sequence shown in FIGS. 3 and 4 is also in principle possible, as well as individual method steps or a plurality of method steps being carried out repeatedly and/or in parallel.

The foregoing relates to the preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims. 

1. A dishwashing machine for commercial use to clean items to be cleaned in a dishwashing chamber cyclically, the dishwashing machine comprising at least one tank for holding a dishwashing liquid, at least one heating apparatus for heating the dishwashing liquid, at least one temperature sensor for detecting the temperature of the dishwashing liquid, and a controller operable to control heating of the dishwashing liquid in at least one program step in a dishwashing program, with the heating being continued at least until a predetermined intended temperature is reached, wherein, before or during an initial heating phase, a start temperature is detected, the minimum heating duration being determined from the start temperature and the heating is carried out accordingly using this minimum duration.
 2. The dishwashing machine as claimed in claim 1, wherein the controller is operable to detect a temperature of the dishwashing liquid once again after the minimum duration has elapsed, and in order to carry out a decision step, in which case, if the temperature is below the intended temperature or is below the intended temperature by more than a tolerance threshold, the heating is extended, and in which case, if the temperature has reached or exceeded the intended temperature, the heating is ended.
 3. The dishwashing machine as claimed in claim 2, wherein the controller is operable to carry out the temperature detection and the decision step once again if the temperature in the respective preceding decision step was below the intended temperature, or was below the intended temperature by more than a tolerance threshold.
 4. The dishwashing machine as claimed in claim 1, wherein the controller is operable to determine the minimum duration analytically or semi-empirically, with the amount of liquid in the dishwashing liquid to be heated, the thermal capacity of the dishwashing liquid to be heated, the temperature difference between the intended temperature and the start temperature, and the heating power of the heating apparatus being sensed and used as initial variables in this determination process.
 5. The dishwashing machine as claimed in claim 4, wherein the controller applies a correction value as a further initial variable, the correction value being designed in order to take account of any thermal loss from the dishwashing liquid during the heating process.
 6. The dishwashing machine as claimed in claim 5, wherein the correction variable is a temperature-dependent correction variable.
 7. The dishwashing machine as claimed in claim 4, wherein the correction variable comprises at least one of the following variables: a correction factor, a correction function; a correction characteristic.
 8. The dishwashing machine as claimed in claim 5, wherein the correction variable is stored in an electronic data memory.
 9. The dishwashing machine as claimed in claim 1, further comprising a circulation device for initial cleaning of the items to be cleared, and at least one final washing tank.
 10. The dishwashing machine as claimed in claim 9, wherein the at least one program step comprises a circulation step, and wherein the heating process is continued at least until the predetermined intended temperature in the washing tank is reached.
 11. The dishwashing machine as claimed in claim 10, wherein the controller detects the start temperature with a predetermined start delay with respect to the start of the circulation step.
 12. The dishwashing machine as claimed in claim 11, wherein the delay is in the range between 5 and 60 seconds, and preferably in the range between 10 and 20 seconds.
 13. The dishwashing machine as claimed in claim 10, wherein the controller is operable to continue the circulation step at least for a predetermined action time after the intended temperature has been reached.
 14. The dishwashing machine as claimed in claim 9, wherein the controller is operable to control heating a final washing liquid in the final washing tank during a circulation step.
 15. The dishwashing machine as claimed in claim 14, wherein the controller is operable to define the duration of the circulation step in accordance with the specific minimum duration of the heating of the final washing liquid.
 16. The dishwashing machine as claimed in claim 15, wherein the controller lengthens the duration of the circulation step in the decision step when the temperature of the final washing liquid (138) is below the intended temperature or is below the intended temperature by more than a tolerance threshold.
 17. The dishwashing machine as claimed in claim 9, further comprising a pressure increasing pump for increasing the pressure of the final washing liquid during the final washing process and/or a fresh water connection for supplying pressurized fresh water to the final washing tank in order to increase the pressure during the final washing process.
 18. A method for controlling a dishwashing machine for commercial use, the method comprising heating dishwashing liquid in at least one tank in at least one program step in a dishwashing program, continuing the heating process at least until a predetermined intended temperature is reached, detecting a start temperature before or during an initial heating phase, determining the minimum heating duration from the start temperature, and heating the dishwashing liquid during this minimum duration.
 19. The method as claimed in claim 18, further comprising again detecting the temperature of the dishwashing liquid after the minimum duration has elapsed and step being carried out, in which case, if the temperature is below the intended temperature or is below the intended temperature by more than a tolerance threshold, extending the heating, or if the temperature has reached or exceeded the intended temperature, ending the heating.
 20. The method as claimed in claim 19, with the temperature detection and the process of carrying out the decision step being carried out repeatedly if the temperature in the respective preceding decision step was below the intended temperature, was below the intended temperature, or was below the intended temperature by more than a tolerance threshold. 